Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus.
Perforating and fracturing applications in a well, which occurs generally during well completion, constitute one such area where significant amounts of time and effort are spent, particularly as increases in well depths and sophisticated architecture are encountered. These applications can involve the positioning of a bridge plug assembly (referred to herein as a “plug”) downhole of a well section or interval to be perforated and fractured. Positioning of the plug may be aided by pumping a driving fluid through the well. This may be particularly helpful where the plug is being advanced through a horizontal section of the well.
Once in place, equipment may communicate with the plug so as to direct setting of the plug. Such setting may include expanding slips and one or more seal members of the plug for anchoring and sealing of the plug, respectively. Once anchored and sealed, a perforation application may take place above the plug so as to provide perforations through the casing in the well interval. Similarly, a fracturing application may follow that directs fracturing fluid under high pressure through the casing perforations and into the adjacent formation, which causes hydraulic fracturing of the reservoir rock of the adjacent formation that is intended to release oil or gas trapped in the reservoir rock such that it flows into the well for easier production. The fracturing fluid typically contains a proppant (such as sand) that aids in holding the fractures open after the fracturing application has been completed. This process may be repeated, generally starting from the terminal end (e.g., toe end) of the well and moving uphole interval by interval, until the casing and formation have been configured and treated as desired.
The presence of the plug in the well keeps the high pressure fracturing applications from affecting the well interval below the plug. Indeed, even though the noted applications are likely to generate well over 5,000 psi, the well interval below the plug is kept hydraulically isolated from the interval thereabove. Due to the high pressure nature of the fracturing and the degree of anchoring required of the plug, it is generally configured for near permanent placement once set. As a result, removal of the plug requires follow on milling out of the plug. Depending on the particular architecture of the well, several plug mill-outs may take place over the course of conventional perforating and fracturing applications for a given well.
As noted above, it is commonplace for a well to be partitioned into a number of intervals. Short sections of unperforated casing can be located between intervals to enable the plugs to be set for isolation of the respective intervals for perforation and fracturing of the respective intervals. Note that not all intervals of the well can contribute equally to the production of hydrocarbons from the well as the petrophysical and geomechanical properties of the reservoir can vary along the length of the well.
Current workflows used to evaluate the productivity of individual intervals of the well are based on two main techniques. The first workflow, commonly described as production logging, is based on the downhole measurements of fluid properties using spinners and pressure measurement. This first workflow requires a tool to be run in the well after milling-out all of the plugs, thus increasing the cost of the well. The second workflow is based on the measurement of tracer concentration. Different tracers are injected into the reservoir with the fracturing fluid over the intervals of the well. The tracers are produced from well with the fracturing fluid and/or hydrocarbons during the initial production of the well. The amount of each given tracer that is produced is a function of the flow contribution of the respective interval in which the given tracer was placed. The use of the multiple different tracers allows for the evaluation of the flow contributions over the number of intervals of the well. Beyond the limitation inherent to the interpretation of the produced fluids (including the tracers, the fracturing fluid and/or hydrocarbons), this second workflow has a limitation in the number of tracers that can be placed into the intervals of a single well as well as the detection of the tracers in the produced fluids.